Final answer:
The quantity demanded of songs when spending $120 at an online music store is 100 songs.
Step-by-step explanation:
In this case, the student spent $120 on songs at an online music store. Since the store charges $1.20 per song, we can calculate the quantity demanded by dividing the total amount spent by the price per song. So, $120 divided by $1.20 equals 100 songs. Therefore, the correct answer is C. The quantity demanded was 100 songs.